1. Field of the Invention
The present invention relates to a plasma display panel, and more particularly to an alternating current surface discharge plasma display panel having an asymmetrical plane electrode structure.
2. Description of the Related Art
The plasma display panel has been known as a thin flat screen display device having a large screen size and a large capacity. Electrons are accelerated by an electric field so that the accelerated electrons have collisions to a discharge gas to cause excitation and subsequent relaxation. This relaxation process causes radiation of an ultraviolet ray. The ultraviolet ray is irradiated onto a fluorescent material, whereby the ultraviolet ray is converted into a visible light. The alternating current plasma display panel is generally superior in luminance, luminous efficiency and operational life-time than the direct current plasma display panel.
FIG. 1 is a perspective view illustrative of a panel structure of a conventional alternating current surface discharge memory type plasma display panel. FIG. 2 is a cross sectional elevation view illustrative of a display cell structure of the conventional alternating current surface discharge memory type plasma display panel of FIG. 1. FIG. 3 is a fragmentary plane view illustrative of the display cell structure of FIG. 2.
The conventional plasma display panel has a front side insulative substrate 1 and a back side insulative substrate 2. A plurality of scanning electrodes 3 and a plurality of sustaining electrodes 4 are provided on an inside face of the front side insulative substrate 1. The scanning electrodes 3 and the sustaining electrodes 4 are alternately aligned at a predetermined pitch in a first horizontal direction. The scanning electrodes 3 and the sustaining electrodes 4 have stripe shapes. The scanning electrodes 3 and the sustaining electrodes 4 extend in parallel to each other and in a second horizontal direction which is perpendicular to the first horizontal direction.
A plurality of first bus electrodes 5 are laminated on the scanning electrodes 3 for reducing an electrode resistance. The first bus electrodes 5 also have a stripe shape and extends along the scanning electrodes 3. The first bus electrodes 5 have a smaller width than the scanning electrodes 3. Each of the first bus electrodes 5 is aligned to one long side of each of the scanning electrodes 3. A plurality of second bus electrodes 6 are laminated on the sustaining electrodes 4 for reducing an electrode resistance. The second bus electrodes 6 also have a stripe shape and extends along the sustaining electrodes 4. The second bus electrodes 6 have a smaller width than the sustaining electrodes 4. Each of the second bus electrodes 6 is aligned to one long side of each of the sustaining electrodes 4.
A plurality of data electrodes 7 are provided on an inside face of the back side insulative substrate 2. The data electrodes 7 are aligned at a predetermined constant pitch in the second horizontal direction. The data electrodes 7 have a stripe shape. The data electrodes 7 extend in parallel to each other and in the first horizontal direction which is perpendicular to the second horizontal direction along which the scanning electrodes 3 and the sustaining electrodes 4 extend.
A discharge gas is filled within an inter-space 8 defined between the front side insulative substrate 1 and the back side insulative substrate 2. The discharge gas may be a helium gas, a neon gas, a xenon gas or a mixture gas thereof.
A first dielectric layer 10 is provided on the inside face of the front side insulative substrate 1, so that the scanning electrodes 3, the sustaining electrodes 4, the first bus electrodes 5 and the second bus electrodes 6 are buried in the first dielectric layer 10. A protection layer 11 is provided on an inside face of the first dielectric layer 10 for protecting the dielectric layer 10 from the discharge. The protection layer 11 may optically comprise magnesium oxide.
A second dielectric layer 12 is provided on the inside face of the back side insulative substrate 2, so that the data electrodes 7 are buried in the first dielectric layer 10. A plurality of separation walls 13 are provided on an inside face of the second dielectric layer 12. The separation walls 13 extend in straight in parallel to each other and in the first horizontal direction, so that the separation walls 13 extend in parallel to the data electrodes 7. In the plane view vertical to the surface of the back side insulative substrate 2, each of the separation walls 13 is positioned between adjacent two of the data electrodes 7, so that each of the data electrodes 7 is positioned under each gap defied between adjacent two of the separation walls 13. The separation walls 13 define plural display cell regions, wherein each of the separation walls 13 separates adjacent two of the plural display cell regions.
A fluorescent material 9 is applied on exposed regions of the inner face of the second dielectric layer 12 and side walls of the separation walls 13, wherein the exposed regions of the inner face of the second dielectric layer 12 are exposed to the plural display cell regions defined by the separation walls 13. The fluorescent material 9 includes two dimensional arrays of three primary colors. The discharge gas generates the ultraviolet ray which is then irradiated onto the fluorescent material 9, whereby the fluorescent material 9 shows the luminescence in accordance with the three primary colors, and a visible light 14 is emitted from an outside surface of the front side insulative substrate 1.
With reference to FIG. 2, the discharge operation of the conventional plasma display panel will be described. A pulse voltage higher than a discharge threshold voltage level is applied across the scanning electrodes 3 and the data electrodes 7 to cause a discharge between the scanning electrodes 3 and the data electrodes 7. In accordance with the polarity of the applied pulse voltage, positive charges and negative charges are forced to move in opposite directions to each other and then accumulated onto respective ones of the first and second dielectric layers 10 and 12.
Equivalent internal voltage or wall voltage causing the respective accumulations of the positive charges and the negative charges has an opposite polarity to the applied pulse voltage, for which reason as the discharge time increases, the effective voltage level in the cell gradually decreases even the applied pulse voltage level remains kept at the constant level. The gradual decease of the effective voltage level results in no longer possible of sustaining the discharge, whereby the discharge will be discontinued in the course of time.
The primary discharge between the scanning electrodes 3 and the data electrodes 7 is caused under another voltage application between the scanning electrodes 3 and the sustaining electrodes 4, so that the primary discharge between the scanning electrodes 3 and the data electrodes 7 serves as a trigger to cause a secondary discharge between the scanning electrodes 3 and the sustaining electrodes 4. This secondary discharge between the scanning electrodes 3 and the sustaining electrodes 4 causes additional respective accumulations of the positive charges and the negative charges on the first dielectric layer 10 such as to cancel the applied voltage.
Subsequently, a sustaining pulse voltage having the same polarity as the wall voltage is further applied between the scanning electrodes 3 and the sustaining electrodes 4, whereby the sustaining pulse voltage is superimposed with the wall voltage. If an amplitude of the sustaining pulse voltage is smaller than the threshold level, the discharge is caused between the scanning electrodes 3 and the sustaining electrodes 4, provided that the effective voltage level as the superimposition of the applied sustaining pulse voltage with the wall voltage is higher than the threshold voltage level. The sustaining pulse voltage is alternately applied between the scanning electrodes 3 and the sustaining electrodes 4, whereby the discharge is sustained. This physical phenomenon corresponds to the memory function.
FIG. 4 is a block diagram illustrative of an entire configuration of the plasma display device including the plasma display panel including a matrix array of the display cell shown in FIG. 2. The plasma display device has a plasma display panel 15. The plasma display panel 15 comprises a dot-matrix array of xe2x80x9cmxnxe2x80x9d of the display cell 16, a plurality of scanning electrodes X1, X2, . . . , Xm extending in the row direction, and a plurality of sustaining electrodes Y1, Y2, . . . , Ym extending in the row direction, and further a plurality of data electrodes D1, D2, . . . Dn extending in the column direction. Namely, the row electrodes comprise the scanning electrodes X1, X2, . . . , Xm and the sustaining electrodes Y1, Y2, . . . , Ym. The column electrodes comprise the data electrodes D1, D2, . . . Dn.
The plasma display device further includes a scanning driver 17 for applying scanning electrode driving voltages to the scanning electrodes X1, X2, . . . , Xm. The plasma display device furthermore includes a sustaining driver 18 for applying sustaining electrode driving voltages to the sustaining electrodes Y1, Y2, . . . , Ym. The plasma display device moreover includes a data driver 19 for applying data electrode driving voltages to the data electrodes D1, D2, . . . Dn.
The plasma display device also includes a control circuit 20 for generating a scanning driver control signal for controlling the scanning driver 17, and a sustaining driver control signal for controlling the sustaining driver 18, as well as a data driver control signal for controlling the data driver 19 based on externally-inputted basic signals, for example, a vertical synchronizing signal Vcync, a horizontal synchronizing signal Hcync, a clock signal Clock and a data signal DATA.
The control circuit 20 further includes a frame memory 20a, a signal processing memory controlling circuit 20b and a driver control circuit 20c. The frame memory 20a stores data signals as image data. The signal processing memory controlling circuit 20b receives the externally-inputted basic signals and generates respective controls signals for controlling the frame memory 20a and the driver control circuit 20c. The driver control circuit 20c generates the scanning driver control signal for controlling the scanning driver 17, and the sustaining driver control signal for controlling the sustaining driver 18, as well as the data driver control signal for controlling the data driver 19.
FIG. 5 is a diagram illustrative of waveforms of scanning electrode driving voltages, sustaining electrode driving voltage and data electrode driving voltage in connection with the plasma display device of FIG. 4. xe2x80x9cWuxe2x80x9d represents the sustaining electrode driving voltage which is commonly applied to the sustaining electrodes Y1, Y2, . . . , Ym. xe2x80x9cWs1xe2x80x9d, xe2x80x9cWs2xe2x80x9d, . . . xe2x80x9cWsmxe2x80x9d represent the scanning electrode driving voltages which are respectively applied to the scanning electrodes X1, X2, . . . , Xm. xe2x80x9cWdxe2x80x9d represents the data electrode driving voltage which is applied to selected one of the data electrodes D1, D2, . . . Dn.
One sub-field corresponds to the one driving cycle. The one sub-field comprises, in the order, a preliminary discharge term xe2x80x9cTpxe2x80x9d, a writing discharge term xe2x80x9cTwxe2x80x9d, a sustaining discharge term xe2x80x9cTsxe2x80x9d and an erasing discharge term xe2x80x9cTexe2x80x9d.
The preliminary discharge term xe2x80x9cTpxe2x80x9dis a term for generating activated particles and wall charges in the discharge gas space 8 for the purpose of obtaining a stable write discharge characteristic in the next write discharge term. After a preliminary discharge pulse xe2x80x9cPpxe2x80x9d has been applied to cause simultaneous discharges in all of the display cells of the plasma display panel, then a preliminary discharge erasing pulse xe2x80x9cPepxe2x80x9d is also simultaneously applied to the scanning electrodes for erasing undesirable charges in the generated wall charges, provided that the undesirable charges may prevent the write discharge and the sustaining discharge.
For example, the preliminary discharge pulse Pp is simultaneously applied to the scanning electrodes X1, X2, . . . , Xm to cause the simultaneous discharges in all of the display cells, before the sustaining electrodes Y1, Y2, . . . , Ym are risen in voltage up to a sustaining voltage level Vs. In order to gradually drop the potential of the sustaining electrodes Y1, Y2, . . . , Ym, the preliminary discharge erasing pulse xe2x80x9cPepxe2x80x9d is applied to the scanning electrodes X1, X2, . . . , Xm for causing an erasing discharge which erase the wall charges or reduces the quantity of the wall charges, wherein the wall charges had been accumulated by the preliminary discharge pulse Pp. The reduction in the quantity of the wall charges has to be made so that the reduced quantity of the wall charges does not prevent the subsequent write discharge and the sustaining discharge.
In the writing discharge term xe2x80x9cTwxe2x80x9d, scanning pulses xe2x80x9cPwxe2x80x9d are sequentially applied to the scanning electrodes X1, X2, . . . , Xm and also in synchronizing with the scanning pulse xe2x80x9cPwxe2x80x9d, a data pulse xe2x80x9cPdxe2x80x9d is selectively applied to a selected data electrode xe2x80x9cDixe2x80x9d (1xe2x89xa6ixe2x89xa6n) of the selected display cell for display, thereby causing the write discharge in the selected cell for the display, and this caused write discharge generates the wall charges.
In the sustaining discharge term xe2x80x9cTsxe2x80x9d, sustaining pulses Pc are applied to the sustaining electrodes Y1, Y2, . . . , Ym, and also phase-delay sustaining pulses Ps, which are delayed in phase by 180 degrees from the sustaining pulses Pc, are applied to the scanning electrodes X1, X2, . . . , Xm, so as to cause a sustaining discharge in the selected display cell for obtaining a desired brightness or luminance, wherein the selected display cell had the write discharge in the writing discharge term xe2x80x9cTwxe2x80x9d.
In the erasing discharge term xe2x80x9cTexe2x80x9d, erasing pulses Pe are applied to the scanning electrodes X1, X2, . . . , Xm to gradually drop the potentials of the scanning electrodes X1, X2, . . . , Xm, so as to cause the erasing discharge, thereby erasing the wall charges or reducing the quantity of the wall charges, wherein the wall charges had accumulated by he sustaining discharge pulse. The reduction in the quantity of the wall charges has to be made so that the reduced quantity of the wall charges does not prevent the subsequent preliminary discharge in the next preliminary discharge term xe2x80x9cTpxe2x80x9d and the writing discharge in the next writing discharge term xe2x80x9cTwxe2x80x9d as well as the sustaining discharge in the next sustaining discharge term xe2x80x9cTsxe2x80x9d in the next cycle.
In the writing discharge term xe2x80x9cTwxe2x80x9d, an opposite discharge between the scanning electrode and the data electrode is likely to be caused. This opposite discharge triggers a surface discharge between the scanning electrodes and the sustaining electrodes. If the opposite discharge and the surface discharge are stable, then input images are correctly displayed. The opposite discharge means the write discharge. The surface discharge means the sustaining discharge.
Japanese laid-open patent publication No. 10-302643 discloses that, in order to obtain a desirable high stability of the write discharge, a width of the scanning electrodes is made narrower than a width of the sustaining electrodes. FIG. 6 is a cress sectional elevation view illustrative of another conventional display cell structure of the plasma display panel disclosed in the above Japanese publication. The conventional display cell structure of FIG. 6 is applied to substantially the same structure as shown in FIG. 1. As shown in FIG. 6, the scanning electrode 3 is smaller in width than the sustaining electrode 4 in order to reduce an overlapping area between the scanning electrode 3 and the data electrode 7. The reduction in the overlapping area between the scanning electrode 3 and the data electrode 7 reduces the likelihood of causing the surface discharge.
The above-described different kinds of the electrodes are different in those roles and also required to have different performances and characteristics. For example, the data electrodes to be applied with signal pulses are required to have such characteristics as to certainly cause the write discharge between the data electrodes and the scanning electrodes, thereby forming a sufficient quantity of the wall charges on the plane electrode in the vicinity of the surface discharge gap.
The scanning electrodes to be applied with the write pulses are required to have such characteristics as to certainly cause the write discharge between the data electrodes and the scanning electrodes, thereby forming the sufficient quantity of the wall charges on the plane electrode in the vicinity of the surface discharge gap, and further additional characteristics so as to allow a prompt transition from the write discharge into the sustaining discharge.
The sustaining electrodes to be applied with the sustaining pulses are required to have such characteristics as to allow a stable and continuous sustaining discharge between the sustaining electrodes and the scanning electrodes.
Not only the surface discharge or the sustaining discharge but also the opposite discharge or the write discharge are likely to be caused in the vicinity of the edge of the surface electrode making the surface discharge gap, dependent upon various factors, for example, the cell structure, the waveforms of the driving voltage pulses and the triggering function due to the electric field strain at the edge of the surface electrodes.
If the write discharge in the vicinity of the edges of the surface electrodes is essential without any unnecessary discharge at the unnecessary region, then this contributes to cause the subsequent sustaining discharge. As a result, the operational margin is made wide and the display quality is improved.
If the write voltage or the potential difference between the data electrodes and the scanning electrodes is low, then it is possible that the write discharge is caused only in the vicinity of the edges of the surface electrodes. Notwithstanding, this write discharge is a weak discharge having a low degree of ionization, thereby forming an insufficient quantity of the wall charges for prompt transition from the write discharge to the sustaining discharge.
If the write voltage or the potential difference between the data electrodes and the scanning electrodes is increased to cause the strong discharge having a high degree of ionization, then an insufficient quantity of the wall charges is formed for prompt transition from the write discharge to the sustaining discharge. This strong write discharge is likely to be spread over the entirety of the surface electrode, whereby a large quantity of the wall charges is formed on the unnecessary area other than the edges of the surface electrode.
FIG. 7 is a schematic view of the opposite discharge or the write discharge between the data electrode and the scanning electrode shown in FIG. 2. In FIG. 7, the surface discharge or the sustaining discharge is not illustrated.
Once the large quantity of the wall charges is formed over the entirety of the surface electrode, the wall charges on the surface electrodes provide an undesirable influence to adjacent cells, thereby causing a discharge interference. This discharge interference may cause erroneous light-on and light-off. To avoid the erroneous light-on and light-off, it is necessary to narrow the operational voltage range. The unnecessary charge and discharge are increased in connection with the write discharge, resulting in an increased power consumption.
If the sustaining voltage level or a potential difference between the sustaining electrodes and the scanning electrodes is increased in place of increasing the write voltage, then undesirable discharges are likely to be caused in non-selected cells. To avoid these undesirable discharges, it is necessary to narrow the operational voltage range. The unnecessary charge and discharge are increased in connection with the write discharge, resulting in an increased power consumption.
Accordingly, it is desirable that a relatively strong write discharge is caused between the data electrode and the edge of the scanning electrode.
As described above, the conventional cell structure of FIG. 6 has the scanning electrode 3 with a reduced width in order to suppress the variation of the position of the discharge generation over the scanning electrode 3, thereby allowing the prompt transition from the opposite discharge as the write discharge into the surface discharge as the sustaining discharge. This structure also suppresses the desirable spread of the sustaining discharge. FIG. 8A is a schematic cross sectional view of the surface discharge or the sustaining discharge between the sustaining electrode and the scanning electrode shown in FIG. 6, wherein the sustaining electrode 4 has a potential of 0(V), whilst the scanning electrode 3 has a potential of Vs(V). FIG. 8B is a schematic cross sectional view of the surface discharge or the sustaining discharge between the sustaining electrode and the scanning electrode shown in FIG. 6, wherein the sustaining electrode 4 has a potential of Vs(V), whilst the scanning electrode 3 has a potential of 0(V). The wall charges are generated after generation of the sustaining discharge.
As shown in FIGS. 8A and 8B, the spread of the sustaining discharge extend to the distanced edges of the sustaining electrode 4 and the scanning electrode 3. The sustaining discharge generates an isotropically radiating ultraviolet ray, whereby the fluorescent material on the outside region of the display cell region is unnecessarily irradiated with a small part of the isotropically radiating ultraviolet ray, and the fluorescent material on the outside region emits a weak visible light of a low luminance.
It is desirable that the sustaining discharge is widely spread over the entirety of the display cell in order to obtain a possible high brightness or luminance. The spread of the sustaining discharge is excessively wide, thereby causing a discharge interference. This discharge interference may cause erroneous light-on and light-off. It is not preferable that the scanning electrodes 3 and the sustaining electrodes 4 as the surface electrodes extend unnecessary toward the boundary with the adjacent cells.
If the electrode area in the vicinity of the surface discharge gap is excessively small, then the insufficient quantity of the wall charges is formed, resulting in undesirable increase of the sustaining voltage and narrowing the available voltage range for performing the required memory function. It is preferable that the sustaining electrode is larger than the scanning electrode in the area in the vicinity of the surface discharge gap in order to make it easy to cause the sustaining discharge subsequent to the write discharge.
In order to obtain the desirable display quality, there are important respective performances of the different kinds of the electrodes, for example, the data electrodes, and the scanning electrodes as well as the sustaining electrodes. For example, the scanning electrodes are operated for both the write discharge and the sustaining discharge, whilst the sustaining electrodes are operated for only the sustaining discharge. The scanning electrodes and the sustaining electrodes are different from each other in the required function or role. It is preferable that the scanning electrodes and the sustaining electrodes are differently designed in consideration of the respective different roles. However, the conventional cell structure of the plasma display panel have the uniform structure for the scanning electrodes 3 and the sustaining electrodes 4 as shown in FIG. 2. This conventional structure makes it difficult that the electrodes exhibit optimum respective performances in the different roles.
In the above circumstances, the development of a novel plasma display panel free from the above problems is desirable.
Accordingly, it is an object of the present invention to provide a novel plasma display panel free from the above problems.
It is a further object of the present invention to provide a novel plasma display panel improved in display quality.
It is a still further object of the present invention to provide a novel plasma display panel having an improved cell structure free from the above problems.
It is yet a further object of the present invention to provide a novel plasma display panel having an improved cell structure for obtaining an improved display quality.
The present invention provides a plasma display panel comprising: a first substrate having a first inside face; a second substrate having a second inside face which confronts the first inside face of the first substrate; a plurality of data electrodes extending over the second inside face of the second substrate in a first horizontal direction; a plurality of separation walls extending over the second inside face of the second substrate in the first horizontal direction, and each of the separation walls separating adjacent two of the data electrodes; a plurality of scanning electrode alignments extending over the first inside face of the first substrate in a second horizontal direction; a plurality of sustaining electrode alignments extending over the second inside face of the second substrate in the second horizontal direction; and the scanning electrode alignments and the sustaining electrode alignments being alternately placed in the first horizontal direction, wherein each of the scanning electrode alignments further includes a plurality of scanning electrodes which are aligned with a predetermined constant gap in the second horizontal direction, and which are electrically connected to each other through a first electrode interconnection, and adjacent two of the scanning electrodes included in each of the scanning electrode alignments are separated from each other by the separation wall, wherein each of the sustaining electrode alignments further includes a plurality of sustaining electrodes which are aligned with the predetermined constant gap in the second horizontal direction, and the sustaining electrodes being electrically connected to each other through a second electrode interconnection, and adjacent two of the sustaining electrodes included in each of the scanning electrode alignments are also separated from each other by the separation wall, and wherein the plasma display panel includes a two-dimensional array of cells, and each of the cells includes a pair of the sustaining electrode and the scanning electrode, and the paired sustaining and scanning electrodes are distanced by a surface discharge gap.
The above and other objects, features and advantages of the present invention will be apparent from the following descriptions.